The present invention relates to electric plugs, and more particularly to such plugs incorporating integral over-current protection such as circuit breakers.
A wide variety of devices have been developed for providing over-current protection at the electric plug. One such approach is to provide a circuit breaker box interposed between a conventional electric plug and a conventional outlet receptacle. This device is disclosed in U.S. Pat. No. 4,484,185, issued Nov. 20, 1984, to Graves entitled SAFETY PLUG ADAPTOR. However, such devices protrude excessively from the outlet, creating safety problems and preventing appliances from being placed against the wall in which the plug is mounted. Further, the necessity of a separate box creates inventory and installation problems. Third, the box must be secured to the receptacle cover plate further complicating the construction and use of this device.
A second type of electric safety plug is illustrated in U.S. Pat. Nos. 4,086,643 and Des. 246,241 issued Apr. 25, 1978 and Nov. 1, 1977, respectively, to Jacobs, entitled COMBINATION PLUG AND POWER CUT-OFF UNIT. This plug includes a hollow multi-piece housing which supports the power cord connection, a circuit breaker, and the prong assembly. The breaker trips whenever excessive current is conducted through the prongs. This plug also suffers several disadvantages. First, its profile is excessively large so that the assembly protrudes undesirably from the receptacle. Second, the multi-piece housing can come open exposing dangerous electric connections. Third, the many pieces required to assemble this plug create inventory and assembly problems.
A third type of electric safety plug is sold by The Belden Division of Cooper Industries located in Geneva, Ill. This plug includes a plug body integrally molded over the end of a power cord and integrally supporting common and ground prongs. The housing also defines a bayonet fuse socket. A bayonet fuse with an integral power prong mounted thereon is releasably secured within the socket. If excessive current flows through the power prong, the integral fuse blows and power is interrupted. To reestablish the connection, the plug must be withdrawn from the outlet; the bayonet fuse must be removed; a proper bayonet replacement fuse must be located and reinstalled within the plug housing; and the plug must be reinserted into the outlet. This plug has several drawbacks. First, the plug must be removed from the receptacle each time the fuse is to be checked or replaced. Second, an inventory of fuses must be maintained to provide replacement capability. Third, the plug is relatively expensive to operate since the fuse-and-prong assembly must continually be replaced.